Introduction to Data Bases

What is (are) Data Information? - no Information is PROCESSED data Data are facts - descriptions of an entity, Entity -> Me Facts -> Name, Address, Phone, Age, Ht, Wt, IQ, Eye, Hair Facts can be related or unrelated Name -> First, Last, MI Address -> Str#, Street, City, State, Zip

Data (cont.) Facts can be Unique to an entity (SSAN) Facts can group people (City, Zip, Eye Color, Income) Facts give information, but must be processed - Relate to an entity: SSAN->Individual - Counted: Population of a state - Ordered: Names in a telephone book - Searched: Finding the people on a street with children - Segregated: Finding registered voters in a district

Levels of Data Bit - 1's & 0's, Computers think in it Character - One or more Bits Field - One or more Characters, max size important Record - One or more Fields, Single field data file is a list File - One or more Records, (Draw flat file example) (N, SS#, Ph) (Note) Here is where most folks stop

Data Base - One or more files - Why more than one file? Different sources List of names and address of students - List of Grades from each class - Merged to form...Report Cards Info not achievable otherwise - List of names & Defaulted Loans - List of voter registrations - Result is recovery of money

Other Terms Data Banks: Groups of Data Bases DBMS: Data Base Management System Keys: The order that records are sorted/searched. Can be more than one –Primary Key: Should be unique to each record –Secondary Key(s) –Compound Keys: Eg. LName FName MI

Other Terms (cont.) Types of Data –Text: Sorts/Queries based on ASCII values of characters

ASCII Table

Other Terms (cont.) Types of Data –Text: Sorts/Queries based on ASCII values of characters –Number: Math functions can be performed on these values –Date: Based on number of days since 12/31/1899 Days can be added or subtracted forming new dates (Eg: 01/01/ = 01/08/2006) DBMS: Data Base Management System

The Relational Model –Data is stored on “Tables” of fixed-length records –Portions of records called “Fields” –Similar fields in different files can be “Related” Individual records in different files can be linked based on data in “Related” fields being identical –Very Flexible, Relations created “On-The-Fly” –Makes Cross-referencing possible Tickets IssuedDriver’s Licences Tic# Date DL#DL# Name Address /1/ Doe 151 Main

Other Terms (cont.) Queries –Method for selecting records that fit a criteria given –Eg: List all the records where the Last Name begins with the letter S –In MS Access LName (assuming that’s what you named the field) in the Field Box “S*” in the Criteria Box “*S*” for a sliding match (field contains the letter S) –Queries Need three elements

A Table: where you are looking

A Criteria: what you want

A Report: how you want it to look